Ziegler Natta type catalysts used for polymerization of alpha-olefin usually involve a procatalyst comprising titanium, magnesium, chlorine, an internal donor and a cocatalyst which is essentially an organo aluminium compound. The performance of such catalysts is further complemented by the usage of an external electron donor.
The procatalysts are usually synthesised by contacting magnesium alkoxide with a mixed solvent (a mixture of TiCl4 and chlorobenzene) in the presence of an internal donor, in multiple stages, adding fresh TiCl4 during each stage. During such synthesis, a compound of the formula TiCl3OR (where R is an alkyl or aryl group) is formed along with solid product. TiCl3OR remain dissolved in the mixed solvent as a contaminant. Such contaminated solvents raise waste disposal issues and therefore the contaminant need to be eliminated. The contaminants in the solvents are most commonly removed by distillation process. The process of distillation is, however, energy intensive, require elaborate equipments and the distillation by itself generate hazardous wastes. U.S. Pat. No. 4,683,215 describes a process for synthesis of Ziegler Natta procatalyst in which the TiCl3OR contaminant in used mixed solvent is removed by treatment with benzoyl chloride which converts TiCl3OR to a solid addition complex. Further, the complex is separated off from the liquid phase and the liquid phase, after removal of the complex is added with fresh TiCl4 and is used to treat the solid mixture containing magnesium ethoxide and the procatalyst product.
However, purification of effluent after each stage, in a multistage reaction of magnesium alkoxide with mixed solvent, is rather cumbersome and fresh solvents used each time after purification would build up solvent inventory. Additionally, TiCl3OR contaminant accumulates after each purification step and the accumulated contaminant would raise waste disposal issues.
There is a need for a process for preparation of Ziegler Natta procatalyst which overcomes the above mentioned disadvantages